Fix ontology selector defaults, add bypass mode, enforce domain/range (#929)

- Align similarity_threshold default to 0.3 everywhere (class signature
  had stale 0.7). Fix matching contradiction in tech-spec.
- Add bypass_selector_below parameter (default 5) to skip vector
  similarity selection when ontology element count is small enough.
- Enforce domain/range constraints in TripleConverter for object
  properties and datatype properties, with subclass hierarchy support.
  Properties with no declared domain/range pass through unchanged.
- Add unit tests for domain/range validation, subclass acceptance,
  polymorphic pass-through, and selector bypass.

Fixes #908, #920

docs/tech-specs/ontorag.md

@@ -278,7 +278,7 @@ The system uses **FAISS (Facebook AI Similarity Search)** with IndexFlatIP for e
 3. **Similarity Search**:
    - For each text segment embedding, search the vector store
    - Retrieve top-k (e.g., 10) most similar ontology elements
-   - Apply similarity threshold (e.g., 0.7) to filter weak matches
+   - Apply similarity threshold (e.g., 0.3) to filter weak matches
    - Aggregate results across all segments, tracking match frequencies
 
 4. **Dependency Resolution**: